Paris Brown has apologised for causing offence with the messages she posted on Twitter between the ages of 14 and 16. Photograph: Gareth Fuller/PA

No further action is to be taken against Britain's first youth police and crime commissioner, who stepped down from the role over offensive comments she made on Twitter, police have said.

Paris Brown, 17, was meant to be providing young people's views on policing but found her tweets being investigated amid claims they were homophobic, racist and violent.

A spokeswoman for Kent police said on Sunday: "We have spoken to the CPS about our findings, and given them our view that this case does not pass the evidential threshold for prosecution; we will make no recommendations to them for charges and will take no further police action having discharged our duty to investigate.

"Whilst some of the language used is offensive, particularly the comments which derogatorily refer to particular social groups, we do not believe that in the context they are grossly offensive on a reasonable objective assessment considering intent."

Brown, from Sheerness in Kent, who was to earn £15,000 a year from the role, has apologised for causing offence with the messages she posted between the ages of 14 and 16.

She denied being homophobic or racist, and said she was against taking drugs, insisting that a reference on Twitter to making "hash brownies" was from a Scooby Doo film. The tweets have been deleted.

The teenager's Twitter account was not checked as part of the recruitment process.

Her questioning by officers came after the force received more than 50 complaints from members of the public that the tweets were homophobic, racist and violent.

Her lawyers, Olswang, have written to Chief Constable Ian Learmonth about the scope and nature of the investigation, including the decision to seize her phone and for the Special Branch to question her.

They said she was visited by a Special Branch officer at her home on 11 April, along with a second officer, and asked to surrender her mobile for inspection. Then she was requested to attend an interview under caution on 14 April.

She was interrogated for an hour and seven minutes about material posted on her Twitter account that had been published in the media. Her phone was returned three days later.

Her lawyers said: "As we are sure that you will readily understand, being subject to a police investigation is highly distressing for any person, but especially so for a teenager, particularly one who has been recently subject to such adverse media coverage.

"In such circumstances, we believe that the police must weigh carefully the extent to which an investigation relating solely to social media activity is merited."

Olswang also referred to the interim guidelines from the director of public prosecutions, Keir Starmer, regarding prosecutions relating to social media.

The Kent police and crime commissioner, Ann Barnes, appointed Brown to the position this month and was to pay £5,000 of the teenager's salary from her own pay.

She praised Brown as a "remarkable young woman" and said her decision not to take up the role, due to begin this summer, was very sad.

Another youth commissioner will be appointed this year, but Barnes said there were lessons to be learned before Brown was replaced.